A seat belt apparatus is attached to a seat of various transport facilities including automobiles in order to hold an occupant and reduce inertial motion of the occupant when a vehicle is in an emergency situation such as a collision. In the emergency situation, the vehicle is largely slowed down compared with in a normal traveling situation. Such a seat belt apparatus typically includes a tongue supported by a seat belt and a buckle fixed to a chassis. The tongue is configured to be inserted into the buckle and engage therewith.
Widely-known buckles (for example, Patent Literature 1) used in conventional seat belt apparatus at least include a latch configured to enter an engaging hole of a tongue so as to engage with the tongue inserted into the buckle, a latch retainer configured to be moved by a biasing force of a spring so as to lock the latch in a locking position of the tongue during an engagement operation of the tongue with the latch, an unlocking operation member configured to unlock the latch locked by the latch retainer and remove the latch from the engaging hole of the tongue to disengage the latch from the tongue, and an ejector configured to push the tongue disengaged from the latch by the unlocking operation member in a direction in which the tongue is removed from the buckle.
In a seat belt apparatus including such a buckle, when the occupant wears the seat belt, the tongue is inserted into the buckle, and the latch engages with the tongue. Thus, the tongue engages with the buckle. As a result, the seat belt is fastened to the occupant such that the occupant is held by the seat belt in the event of an emergency as described above. This reduces the inertial movement of the occupant. The occupant pushes the unlocking operation member to release the seat belt from the occupant. As a result, the latch is disengaged from the tongue.